As last-minute filers complete their Form 1040s or sign balance-due checks to Uncle Sam today, they might wish to pause to acknowledge their contribution to the U.S. armed forces.

Although the figure does not appear in President Reagan's budget or the spending plans under discussion in Congress, about 50 cents of every federal income tax dollar paid by individuals goes for military-related programs, different analyses show.

That could translate to a military tax bill of $1,500 to $2,000 for many single taxpayers and $3,000 to $4,000 or more for two-income couples.

The military claim on income tax receipts, like the military budget, has grown substantially since Reagan took office, according to a study by Paul Murphy, director of Military Spending Research Services, a private firm in Washington.

Murphy calculates that military programs, broadly defined, accounted for 51.4 percent of spending from general budget funds in fiscal 1985. For 1986, the figure rises to 52.7 percent.

Both fiscal years are covered in part by taxes paid in calendar 1985.

The 1986 figure "represents a growth of 15.8 percent in the military's tax dollar share since fiscal 1980," or more than 7 cents on the dollar, according to Murphy's study.

His analysis, "The Military Tax Bite 1986," considers a bigger picture than the so-called defense function of the federal budget. While not totally comprehensive, Murphy's measure of military spending includes most veterans programs, international military assistance, a small portion of space agency spending and a big share of net interest on the public debt.

The resulting sum is considerably larger than what the Office of Management and Budget defines as defense spending -- $396 billion versus $266 billion in 1986.

In determining the military share of income taxes, Murphy uses a reduced budget pie of "federal funds" spending, which excludes programs funded by specially earmarked taxes, such as Social Security.

A similar but more conservative analysis by Marion Anderson, director of Employment Research Associates in Lansing, Mich., determined that military spending will claim 50 cents of each income tax dollar in fiscal 1986 -- more than $175 billion from individual taxpayers.

"People haven't the faintest idea how much they're paying the Pentagon," Anderson said. "I think it's largely because people don't see the money."

According to figures developed by the Washington office of a major accounting firm, a single taxpayer with a $25,000 salary and typical deductions and contributions has a federal income tax bill of about $3,600, with most or all withheld from salary. Thus, that taxpayer may contribute about $1,800 a year for Pentagon spending and other military-related costs.

Comparable military tax figures would be about $2,000 for a one-income couple with $40,000 in salary, $4,350 for a two-income couple with $65,000 in salary and $14,000 for a two-income couple with salaries totaling $120,000.

Applying the formula to the Treasury Department's profile of a median household income family -- a couple with one wage-earner, two children and earnings of $33,600 -- the military tax would be about $1,750.

"As the Pentagon budget has gone up, people have not, on the whole, been cognizant of what it literally costs them," Anderson said. "The Pentagon bills all get paid," she said, "but if the money is borrowed, it's less straightforward."

From another perspective, individual income taxes alone -- an estimated $354 billion in 1986 -- would be insufficient to support the military budget as defined by Murphy. Adding corporate income taxes to the revenue total would meet the figure, but with less than $30 billion to spare for other programs throughout the government.

"Further buildup plans call for increasing the military share of income taxes and general budget funds to 59 percent by 1991," Murphy writes. "Without the generation of new budget revenues this will mean that the squeeze on civilian programs funded with income taxes will become even more severe."